An orthodontic appliance typically comprises a bracket portion having an archwire slot formed therein, which is dimensioned to receive an archwire. The archwire slot extends in the mesial-distal direction of the appliance. Tie-wings project outwardly from either side of the archwire slot. A base member is typically fixed to the underside of the bracket portion. The orthodontic appliance is mounted to a tooth by applying adhesive to the base member and mounting the base member to the face of the tooth. With other types of orthodontic appliances, the bracket portion is welded to a thin metal strip or band. The band is in turn wrapped around the tooth and fixed relative thereto by tooth bonding cement.
The orthodontic archwire is then fitted into the archwire slot and ligated to the orthodontic appliance. Typically, a stainless steel ligature wire or elastic member is fitted under the archwire and wrapped around the tie-wings to ligate the archwire to the appliance. The resultant bending and tension within the wire imparts forces to the appliance which are in turn imparted to the tooth. The archwire must be securely ligated to the orthodontic appliance to move the tooth as desired. The force of the archwire can then be accurately imparted to the appliance and, therefore, accurately imparted to the tooth.
During orthodontic treatment, it is necessary for the orthodontic appliance to be able to move relative to the archwire. The forces imparted by the archwire are intended to move the tooth. Therefore, the appliance, which is firmly attached to the tooth, must be permitted to move with the tooth relative to the archwire. One problem with known orthodontic appliances, however, is that the ligature becomes securely engaged with both the archwire and the appliance. As a result, the appliance cannot move freely with the tooth relative to the archwire during treatment. And, accordingly, the tooth cannot move freely in response to the force of the archwire. The outcome of the orthodontic treatment is unpredictable.
One approach to solving this problem, has been to ligate the archwire to the orthodontic appliance with a stainless steel ligature wire, so that a space is maintained between the ligature wire and the orthodontic archwire. The archwire is then usually permitted to slide relative to the orthodontic appliance to permit tooth movement. One problem with this approach, however, is that it is difficult for the clinician to accurately twist the ligature wire so that an appropriate space is maintained between the ligature wire and the orthodontic archwire. This has also proven to be a relatively time-consuming and, therefore, expensive procedure.
With elastic ligatures, on the other hand, it has not been possible to ligate an archwire in such a way that permits the elastic and orthodontic appliance to move relative to the archwire. It has been difficult, therefore, to achieve free tooth movement with elastic ligatures.
The problem of permitting orthodontic appliances to move relative to an orthodontic archwire is enhanced with ceramic orthodontic appliances. There is typically a greater degree of friction between ceramic surfaces and an orthodontic archwire than between metal surfaces and an orthodontic archwire. This problem is further enhanced with orthodontic archwires that are coated with a polymeric material. The polymeric material tends to further increase the level of friction between the archwire and the ceramic appliances.
It is an object of the present invention, therefore, to provide orthodontic appliances that overcome the problems and disadvantages associated with ligating archwires to known orthodontic appliances.